1. Field of the Invention
The present invention relates to an LCD device and a method for driving the same, and more particularly to, an LCD device and a method for driving the same which can minimize a recording capacity of a frame memory for recording and reading a frame of image data so that the time-sequential LCD device can be driven at a high speed.
2. Description of the Related Art
In general, cathode ray tubes (CRTs) are among the most widely-used display devices, used for measuring instruments and information terminals as well as televisions. However, CRTs are not suited for the small size and light weight requirements of electronic products due to its size and weight.
Therefore, liquid crystal display (LCD) devices having the advantages of small size, light weight and low power consumption, have been developed to replace CRTs.
Driving the LCD device uses the optical anisotropy and polarization properties of liquid crystal. Because the liquid crystal molecule has a round bar shape with a long axis and a short axis, the liquid crystal molecule has direction in its molecular arrangement. The molecular arrangement direction can be controlled by applying an electric field to a group of the liquid crystal molecules.
Accordingly, when the molecular arrangement direction of the liquid crystal molecules are arbitrarily controlled, lights supplied from a back-light installed on a rear surface of an LCD panel are selectively transmitted or intercepted according to the arrangement direction of the liquid crystal molecules. Images can be displayed on the LCD panel on the basis of the principle.
FIG. 1 is a cross-sectional diagram illustrating a conventional LCD device.
Referring to FIG. 1, the LCD device 10 includes a first substrate 20 and a second substrate 40 soldered to face each other with a predetermined cell-gap, a liquid crystal layer 30 formed at the cell-gap between the first substrate 20 and the second substrate 40, and a back-light 50 disposed on the rear surface of the second substrate 40 for supplying lights to an LCD panel 15 consisting of the first substrate 20, the second substrate 40 and the liquid crystal layer 30.
A black matrix 22 made of light intercepting material to divide light transmissible pixels is formed in a mesh shape along the outer edge of the pixels on a bottom surface of a transparent substrate 21 of the first substrate 20. R, G and B color filters 23 are disposed on the bottom surface of the transparent substrate 21 on which the black matrix 22 has been formed, so that lights transmitted from the pixels can have R, G and B color.
A transparent common electrode 24 which is a side electrode for applying an electric field to the liquid crystal layer 30 is formed at the lower portion of the color filter 23.
A thin film transistor (TFT) Ti for performing a switching operation and a transparent pixel electrode 42 for receiving a signal from the TFT T1 and applying an electric field to the liquid crystal layer 30 with the common electrode 24 are disposed at the upper portion of the transparent substrate 41 of the first substrate 40.
In addition, a plurality of gate lines arranged in the horizontal direction at regular intervals and a plurality of data lines arranged in the vertical direction at regular intervals are orthogonal at the upper portion of the transparent substrate 41 of the second substrate 40. Rectangular regions on which the gate lines and the data lines cross each other are defined as pixels. The pixel electrodes 42 are individually formed in the pixels.
The TFT T1 includes a gate electrode electrically connected to the gate lines, a source electrode electrically connected to the data lines, and a drain electrode electrically connected the pixel electrode 42.
However, the related art device has the following problems. First, a transmittance of lights transmitting through the color filter 23 is maximally 33%. That is, the light loss is large. In order to increase the brightness of the LCD device, lights generated by the back-light 50 must be made brighter, which results in higher power consumption.
Second, the color filter 23 is very expensive, increasing the manufacturing cost of the LCD device.
In order to solve the above problems, there has been suggested a time- sequential LCD device which can reproduce full color without the color filter 23.
Generally, when the related art LCD device is driven, the back-light is turned on to supply a white light. However, in the time-sequential LCD device, R, G and B back-lights are sequentially turned on at intervals of a predetermined time in one frame of an image, thereby displaying color images.
As compared with the conventional LCD device, the time-sequential LCD device does not require the color filter but uses the R, G and B back-lights to individually generate R, G and B lights.
The time-sequential LCD device divides one frame of the image into first to third sub-frames, sequentially supplies R, G and B image data of the first to third sub-frames to the LCD panel, and sequentially turns on the R, G and B back-light according to the first to third sub-frames, thereby displaying color images.
Accordingly, the time-sequential LCD device requires a frame memory for recording one frame of the image data and reading the recorded image data, and includes a first frame memory unit for recording odd-numbered frames of the image data and reading the odd-numbered frames of the recorded image data, and a second frame memory unit for recording even-numbered frames of the image data and reading the even-numbered frames of the recorded image data for a high speed driving.
That is, while the odd-numbered frames of the image data are being recorded in the first frame memory unit, the even-numbered frames of the image data are read from the second frame memory unit, and while the odd-numbered frames of the image data are being read from the first frame memory unit, the even-numbered frames of the image data are recorded in the second frame memory unit. As a result, the delay time in recording and reading the frames of the image data can be reduced thereby achieving high speed driving.
However, as described above, the time-sequential LCD device individually includes the first frame memory unit for recording the odd-numbered frames of the image data and reading the odd-numbered frames of the recorded image data, and the second frame memory unit for recording the even-numbered frames of the image data and reading the even-numbered frames of the recorded image data to achieve the high speed driving. Accordingly, the time-sequential LCD device requires a frame memory having a large recording capacity, which increases the cost of production.